The easiest way to check AIR flow through the radiator fins is by tilting it directly at the sun. A surface with a smooth color is better, but areas where air (light) is blocked are still apparent. The center is usually clearest because the evaporator fins catch most of that trash, but debris can go around the sides & get into the radiator fins near the tanks.
To check coolant flow:
To keep most trash out of all the fins:
